Anterior cervical discectomy with fusion is an operation that involves relieving the pressure placed on nerve roots and the spinal cord by a herniated disc or bone spurs. This condition is referred to as nerve root compression. The procedure includes removing the damaged intervertebral disc, which is usually the source of the compression and placing a bone graft between vertebrae adjacent to the space left by the removed disc. The bone graft is commonly an inter-vertebral-body cage filled with bone (or BMP-soaked sponges, etc.). Commonly, a vertebral plate is used to stabilize the spine and contain the intra-body cage while the spine heals.
There are currently numerous plates used for the process of internal fixation in the cervical spine. Some have locking screws and some have variable angle or axis screws and others have a mixture of both of the above. A common problem with the use of any cervical plate in conjunction with inter-body cages is that the cages telescope or subside into adjacent vertebral bodies on a delayed basis after surgery. This is due to a variety of factors including differences in biomechanical properties of the cage in relation to the vertebral body, inadvertent destruction of the end plate during end plate preparation, poor bone quality and micromotion, among others. If subsidence becomes too great, screws will break and the plate will fail.
A second problem is that the superior vertebral body may translocate anteriorly on a rotational basis, with the anterior inferior cage serving as the fulcrum; anterior rotational translocation. Even with locking screws in the inferior aspect of current plates, this anterior rotational translocation is not prevented.
A third method of cage and fusion failure is due to inadvertent creation of a gap between the interbody cage filled with bone (or BMP-soaked sponges, etc.) and the vertebral body end plate. A method to reduce this gap intraoperatively, using a (“lag screw”) compression from the plate to the vertebral body that reduces this gap, would minimize this problem. In addition, compression across a fusion mass is known to increase fusion rate, as bone fuses under compressive loads at a higher rate.